netdev - Re: [PATCH net-next 2/2] net: cls_u32: Add support for skip-sw flag to tc u32 classifier.

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Message-ID: <5733C3F7.1060800@intel.com>
Date:	Wed, 11 May 2016 16:44:55 -0700
From:	"Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:	David Miller <davem@...emloft.net>
CC:	john.r.fastabend@...el.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: cls_u32: Add support for skip-sw flag
 to tc u32 classifier.

On 5/11/2016 4:23 PM, David Miller wrote:
> From: Sridhar Samudrala <sridhar.samudrala@...el.com>
> Date: Mon,  9 May 2016 12:18:44 -0700
>
>> On devices that support TC U32 offloads, this flag enables a filter to be
>> added only to HW. skip-sw and skip-hw are mutually exclusive flags. By
>> default without any flags, the filter is added to both HW and SW, but no
>> error checks are done in case of failure to add to HW. With skip-sw,
>> failure to add to HW is treated as an error.
> I really want you to provide a "[PATCH net-next 0/2]" header posting
> explaining what this series is doing, and why.

Sure. Will submit a v2 with a header patch in a day or so after waiting 
for any other comments.

>
> This is a core semantic issue, and we have to make sure all amongst us
> that we are all comfortable with exporting the offloadability controls
> in the way you are implementing them.

I tried to implement the semantics based on an earlier discussion about 
these flags in this
email thread.
     http://thread.gmane.org/gmane.linux.network/401733

>
> Also:
>
>> @@ -871,10 +889,15 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
>>   			return err;
>>   		}
>>   
>> +		err = u32_replace_hw_knode(tp, new, flags);
>> +		if (err) {
>> +			u32_destroy_key(tp, new, false);
>> +			return err;
>> +		}
>> +
>>   		u32_replace_knode(tp, tp_c, new);
>>   		tcf_unbind_filter(tp, &n->res);
>>   		call_rcu(&n->rcu, u32_delete_key_rcu);
>> -		u32_replace_hw_knode(tp, new, flags);
>>   		return 0;
>>   	}
>>   
> Are you sure this reordering is OK?

I think so. This reordering is required to support skip-sw semantic of 
returning error in case of failure to add to hardware.
It doesn't break the default semantics of adding to both hw and sw as 
u32_replace_hw_knode() will not return err if skip-sw is not set.

Thanks
Sridhar